CILIARY MECHANISMS OF LAMELLIBRANCHS 665 
of the mouth and palps of the left side have been twisted to the 
right, so that the former (m) opens toward the observer, and the 
entire extent of oral grooves (0g) is seen at once. The foot (f), 
instead of being united with the visceral mass (vms) lies to the 
right of it, and is attached to the under side of the byssus (bs). 
There is a deep groove along its right side. If this is a byssus 
groove, the right is morphologically its ventral side. The gill 
of the left side (gl) is removed some distance from the visceral 
mass and is suspended by a membrane from the mantle wall. 
Just dorsal to the line of attachment, the mantle is thickened 
into very large, white folds (wf), structures not seen elsewhere, 
and perhaps containing extensions of the sexual mass. Around 
the edge of the mantle, a wide, thin fold arises perpendicularly 
from it, and extends inward, precisely as in Pecten. 
Cills. The ciliation of the gill (fig. 34, gl) is different, in many 
respects, from that of all other gills examined. Figure 35 
represents an enlarged portion of the inner left demibranch, 
showing its inner lamella, the suspending membrane (gm), and 
the white folds of the mantle (wf). The ciliation of all lamellae 
is like this. The thickened base of the lamella (fb) is free. 
Running parallel to this, there seems to be a line of division (dot- 
ted line x) of cilia streams on the lamella, material coming to its 
surface between this region and the base, being carried to the 
base and forward to the free ends of the palps. If in small 
Fig. 36 Tagelus californianus; ap, anterior palp; b, bay of mantle; f, foot; 
7g, inner demibranch of gill; m, mantle wall; pp, posterior palp; s, siphons. 
Fig. 37 Tagelus californianus; detail of palp ciliation; dm, dorsal margin of 
palp; ly, lateral oral groove; vm, ventral margin of palp; other letters as in figure 
36. 
Fig. 388 Cardium corbis; d7, distal oral groove; og, outer demibranch of gill; 
other letters as in figures 36 and 37. 
Fig. 39 Chama exogyra; aa, anterior adductor; 6, bay of mantle; es, excur- 
rent tube of siphon; f, foot; fo, foot opening of mantle; 7g, inner demibranch of 
gill; 7s, incurrent tube of siphon; m, mantle wall; og, outer demibranch of gill; 
p, anterior palp; pa, posterior adductor; sl, shell ligament; vms, visceral mass. 
Fig. 40 Chama exogyra; detail of ciliation of gills, palps and visceral mass; 
ap, anterior palp; lg, lateral oral groove; pp, posterior palp; other letters as in 
figure 30. 
Fig. 41 Chama exogyra; lg, lateral oral groove; pg, proximal oral groove; 
mo, mouth. 
